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A363925
Expansion of Sum_{k>0} x^k / (1 - x^(5*k))^2.
5
1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 4, 3, 1, 1, 1, 5, 1, 3, 1, 1, 6, 4, 1, 3, 1, 7, 1, 1, 1, 3, 8, 5, 4, 1, 1, 11, 1, 1, 1, 1, 10, 8, 1, 4, 1, 11, 1, 7, 1, 1, 12, 7, 1, 3, 4, 13, 1, 1, 1, 3, 14, 8, 6, 5, 1, 20, 1, 1, 1, 1, 16, 11, 1, 1, 1, 17, 4, 9, 1, 5, 18, 10, 1, 8, 1, 19, 1, 4, 1, 3, 20, 11
OFFSET
1,6
LINKS
FORMULA
a(n) = (1/5) * Sum_{d|n, d==1 mod 5} (d+4) = (4 * A001876(n) + A284097(n))/5.
G.f.: Sum_{k>0} k * x^(5*k-4) / (1 - x^(5*k-4)).
MATHEMATICA
a[n_] := DivisorSum[n, # + 4 &, Mod[#, 5] == 1 &] / 5; Array[a, 100] (* Amiram Eldar, Jun 28 2023 *)
PROG
(PARI) a(n) = sumdiv(n, d, (d%5==1)*(d+4))/5;
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Jun 28 2023
STATUS
approved